TypeError: unhashable type: 'PosixPath' when collecting conftest

[joshfriend]

Environment details:

• macOS 10.14.6
• python 3.8.5
• pytest 6.2.2

I'm facing a completely inscrutable error which I cannot for the life of me figure out. If I have pathlib.Path as a type hint on a class, I get the following error from pytest:

Traceback (most recent call last):
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/config/__init__.py", line 480, in _importconftest
    return self._conftestpath2mod[key]
KeyError: PosixPath()

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/josh/someproject/.venv/bin/pytest", line 8, in <module>
    sys.exit(main())
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/config/__init__.py", line 90, in main
    config = _prepareconfig(args, plugins)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/config/__init__.py", line 242, in _prepareconfig
    return pluginmanager.hook.pytest_cmdline_parse(
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/hooks.py", line 286, in __call__
    return self._hookexec(self, self.get_hookimpls(), kwargs)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/manager.py", line 93, in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/manager.py", line 84, in <lambda>
    self._inner_hookexec = lambda hook, methods, kwargs: hook.multicall(
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/callers.py", line 203, in _multicall
    gen.send(outcome)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/helpconfig.py", line 90, in pytest_cmdline_parse
    config = outcome.get_result()
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/callers.py", line 80, in get_result
    raise ex[1].with_traceback(ex[2])
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/callers.py", line 187, in _multicall
    res = hook_impl.function(*args)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/config/__init__.py", line 822, in pytest_cmdline_parse
    self.parse(args)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/config/__init__.py", line 1030, in parse
    self._preparse(args, addopts=addopts)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/config/__init__.py", line 987, in _preparse
    self.hook.pytest_load_initial_conftests(
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/hooks.py", line 286, in __call__
    return self._hookexec(self, self.get_hookimpls(), kwargs)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/manager.py", line 93, in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/manager.py", line 84, in <lambda>
    self._inner_hookexec = lambda hook, methods, kwargs: hook.multicall(
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/callers.py", line 208, in _multicall
    return outcome.get_result()
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/callers.py", line 80, in get_result
    raise ex[1].with_traceback(ex[2])
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/pluggy/callers.py", line 187, in _multicall
    res = hook_impl.function(*args)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/config/__init__.py", line 885, in pytest_load_initial_conftests
    self.pluginmanager._set_initial_conftests(early_config.known_args_namespace)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/config/__init__.py", line 426, in _set_initial_conftests
    self._try_load_conftest(anchor)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/config/__init__.py", line 432, in _try_load_conftest
    self._getconftestmodules(anchor)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/config/__init__.py", line 458, in _getconftestmodules
    mod = self._importconftest(conftestpath)
  File "</Users/josh/someproject/.venv/lib/python3.8>/site-packages/_pytest/config/__init__.py", line 498, in _importconftest
    self._conftestpath2mod[key] = mod
TypeError: unhashable type: 'PosixPath'

I have searched the issues list and found a similar error showed up in #6925, but I do not use xdist. If i replace type hints of Path with os.PathLike the problem is "fixed". If i use pathlib.PurePath, I get this error:

Traceback (most recent call last):
  File "/Users/josh/someproject/.venv/bin/pytest", line 8, in <module>
    sys.exit(console_main())
  File "/Users/josh/someproject/.venv/lib/python3.8/site-packages/_pytest/config/__init__.py", line 185, in console_main
    code = main()
  File "/Users/josh/someproject/.venv/lib/python3.8/site-packages/_pytest/config/__init__.py", line 148, in main
    exc_info.traceback = exc_info.traceback.filter(
  File "/Users/josh/someproject/.venv/lib/python3.8/site-packages/_pytest/_code/code.py", line 395, in filter
    return Traceback(filter(fn, self), self._excinfo)
  File "/Users/josh/someproject/.venv/lib/python3.8/site-packages/_pytest/_code/code.py", line 335, in __init__
    super().__init__(tb)
  File "/Users/josh/someproject/.venv/lib/python3.8/site-packages/_pytest/config/__init__.py", line 127, in filter_traceback_for_conftest_import_failure
    return filter_traceback(entry) and "importlib" not in str(entry.path).split(os.sep)
  File "/Users/josh/someproject/.venv/lib/python3.8/site-packages/_pytest/_code/code.py", line 1249, in filter_traceback
    p = Path(entry.path)
TypeError: __init__() takes 1 positional argument but 2 were given

$ pip list
Package               Version
--------------------- -------
apispec               3.3.2
APScheduler           3.7.0
astroid               2.4.2
attrs                 20.3.0
basicauth             0.4.1
bitarray              1.6.3
click                 7.1.2
colorzero             1.1
coverage              5.4
Flask                 1.1.2
Flask-Cors            3.0.10
Flask-SocketIO        4.3.2
freezegun             0.3.15
gevent                21.1.2
gpiozero              1.5.1
greenlet              1.0.0
gunicorn              20.0.4
isort                 5.7.0
itsdangerous          1.1.0
Jinja2                2.11.3
lazy-object-proxy     1.4.3
MarkupSafe            1.1.1
marshmallow           3.10.0
marshmallow-dataclass 6.1.0
mccabe                0.6.1
more-itertools        8.7.0
mypy-extensions       0.4.3
packaging             20.9
pip                   21.0.1
pluggy                0.13.1
py                    1.10.0
PyJWT                 1.7.1
pylint                2.6.0
pylint-flask          0.6
pylint-plugin-utils   0.6
pyparsing             2.4.7
pyserial              3.5
pytest                5.4.3
pytest-cov            2.11.1
pytest-mock           1.13.0
pytest-random-order   1.0.4
python-dateutil       2.8.1
python-engineio       3.14.2
python-socketio       4.6.1
pytz                  2020.5
services              0.1.0
setuptools            52.0.0
simplejson            3.17.2
six                   1.15.0
toml                  0.10.2
typing-extensions     3.7.4.3
typing-inspect        0.6.0
tzlocal               2.1
wcwidth               0.2.5
webargs               5.5.3
Werkzeug              1.0.1
wheel                 0.36.2
wrapt                 1.12.1
zope.event            4.5.0
zope.interface        5.2.0

[The-Compiler]

Could you show the code causing this, rather than describing it?

[joshfriend]

Yeah, sorry. It seems pretty innocuous, adding this to my project causes the unhashable type error:

from pathlib import Path
from dataclasses import dataclass
@dataclass
class Example:
    foo: Path

Can't share the entire project unfortunately, but the reason I think it might have something to do with pytest is that the app runs fine with this code, but test collection blows up with the errors I posted earlier.

[nicoddemus]

Hi @joshfriend,

Thanks for posting an example, however this passes for me (in 5.4.3 and 6.2.2):

λ pytest foo.py --no-header
======================================= test session starts =======================================
collected 0 items

======================================== warnings summary =========================================
foo.py:4
  d:\projects\pytest\.tmp\foo.py:4: PytestCollectionWarning: cannot collect test class 'TestExample' because it has a __init__ constructor (from: foo.py)
    class TestExample:

-- Docs: https://docs.pytest.org/en/stable/warnings.html
======================================= 1 warning in 0.01s ========================================

(I renamed Example to TestExample so pytest would try to collect it as a test).

Can you reproduce the problem in a minimal example, like the one you posted but that fails when executed by pytest?

[Zac-HD]

Closing because there's not much we can do without a reproducing example.